Relatively little work has explored the role of stress and social rhythms (i.e., daily routines) as they impact the circadian system in depression. The goal of this project is to investigate a theoretical model describing pathways by which social factors may be related to depression via their impact on circadian rhythms. After meeting screening criteria, 40 depressed and 40 normal control participants will complete a life events interview. They will be given actillumes (devices which measure sleep/wake activity) and prospective, daily measures of social interactions and mood to complete over a 1-week period of time. For both groups, linear regression will be used to predict social and circadian rhythms from social rhythm disruption (SRD) life events that have occurred within the past 4 months. Cross-sectional analyses utilizing linear and logistic regression will investigate the relationship between circadian and social rhythms and circadian rhythms and depression. It is predicted that individuals with depression are more sensitive and less adaptive to changes in their environment as compared to non-depressed subjects. This project will increase our understanding of psychosocial and biological interactions involved in major depressive disorder. In addition, this study is likely to enhance understanding of the validity of social rhythms as a construct. This line of research may provide guidelines for addressing circadian factors when developing interventions.